In 4x01, Mr. Morden says he requested Londo be relocated to Centauri Prime so that he could serve as his liaison to the royal court. My question is... why? Given that he got a resolution passed giving the Shadows a small continent all on his own, I'm not sure he needs a liaison?

If my memory is correct Mr. Morden didn't get the small continent on his own. He had Lord Rifa as his person in the Royal Court. Now that Londo had him killed Mr. Morden need someone else and that person was Londo.

Of course, Morden still had access to the emperor. It's possible, however, that the emperor isn't actually a member of the royal court and that you'd still need to have a liaison to the royal court even if you had access to the emperor. In support of this is Londo's saying that the regent acted without the support or knowledge or whatever of the royal court after Londo became emperor.